The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Solid state drives (SSDs) are data storage devices that utilize integrated circuit memory to store data. Unlike magnetic and optical disk drives, SSDs do not employ any moving mechanical components. Many SSDs use flash memory, which retains data without power. Other SSDs utilize random-access memory (RAM). RAM-based SSDs may employ separate power sources, such as batteries, to maintain data after power loss.
One limitation of flash memory is that, after a bit has been set to logic zero, the bit can only be reset to logic one by “erasing” an entire block in which the bit is located, where the block includes many kilobytes of data. In other words, in order to re-write a byte of data, many kilobytes of data must first be erased. Erasing a block typically involves setting all bits in the block to logic one. With a freshly erased block, any location within that block can then be programmed.
Another limitation of flash memory is that flash memory degrades after a number of program-erase (P/E) cycles. Some commercially available flash devices are guaranteed to withstand around 100,000 P/E cycles, but then wear begins to deteriorate the integrity of the flash device.